Don't Make This Mistake When Designing Li-ion Battery Circuits!
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- เผยแพร่เมื่อ 2 พ.ค. 2024
- There's tons of crucial aspects of designing a safe and effective lithium ion battery circuit. In this video I cover load sharing, an often overlooked topic in lithium ion battery design.
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Two clarifications:
1) When I spoke of power path IC's I spoke as if all can work in "supplemental mode". Supplemental mode is when charging, the IC can suppliment the wall supply with the battery.
Not 100% of path path IC's can do this. Most can, but some only source power for the load from the wall while charging. Still useful, but not quite as much.
Make sure to always check the datasheet!!!
2) On the second method, the PFET should be two back to back. This prevents the input supply directly charging the battery through the body diode!
This is very informative, please can you give. A part number of such ICs!? Also if possible please create a tutorial on creating on which can supply and charge the battery.
Subbed,
Greetings from Tanzania 🇹🇿
Problem with your second method: The body diode of the PFET is still conducting. So you're charging the battery cell through the schotky + intrinsic body diode. You should put two PFETs back-to-back to fix this.
Ah shoot. Yes you're right, dunno how I missed it... I always use this circuit with the battery going into a boost converter, so I don't worry about it..
Added a note to the pinned comment, and updated the blog post. Really wish YT let us put text pop-ups in the video like they used to..
I’ve seen a version of this circuit on Andreas Speiss’ channel with the P MOSFET drain and source reversed. I think this would stop the battery from being charged by the power path as the body diode is reverse biased?
Based on the title, I thought this was going to say "don't try to charge to lipos in series", but I like this content better and will review this when diving into my next design.
Hah! Not quite :) Glad you enjoyed
Hello ,amazing explanation, I have only one suggestion, I want to see a desk overhead shooting to keep the excellent content matches what we are seeing, and your face of course, because showing only your face most of the time, will be difficult for me to focus on, I want to see more dynamic video where there is many things on the screen , thank you for your efforts and simplicity of the explanation 👌
For those applications where supply interruption is not an issue ( like torches or portable emergency LED lighting ? ) ... by far the simplest arrangement is to avoid the complicated electronics ... and ... just fit a single pole changeover switch ! ! ..so the battery is either connected to the charger or the load , but NEVER both at the same time ! .. This is how I do it ! ( and for those unfamiliar with Lithium batteries NEVER charge more than 4.2 Volts ) ..... ( tried - n - tested ) ..... DAVE™🛑
I just found your channel and I'm going to be going through your backlog for the near future. I'm an EE, recently graduated, and your videos will be able to help me connect the theoretical and basic configurations I learned in school to practical and creative circuits I need to design for work! Good work man! Thanks for the effort you put into these!
This right here. When I had to design battery power with a 5V boost converter, the only schematics I could google were the ones where the whole supply always goes through the linear charge IC, ffs. Ended up with a mess of a set up where I programmatically detect the charger being plugged in and out through two different voltage comparators and switch accordingly. It did end up working, though
Thank you for sharing these. You know it seems like there are lots of information on battery management on the internet but they are very discrete. seems like no one really has figured out the perfect lithium-ion BMS yet.
Got a link to that other video you referenced?
Removable cells & exterior charging problem solved 👏🏻😊
The easiest way to get passed these issues is when using components that have sleep or idle modes. When the components go to sleep the battery will definitely fully charge, without trickle charging.
Awesome video! Clear and concise content with your level-headed demeanor.
Much appreciated!
This was very good, thanks.
I had a brainfart idea of disabling the charging IC over its EN pin (over the MCU that's powered from there lol), but then I realized that I would need a way to detect both battery presence and plugged-in status to even attempt that.
Is it a bad idea to always let the battery be trickle charged if you never allow the battery to exceed 4.0v? Like as a battery backup system that keeps the battery charged.
Very good information, really appreciate the knowledge dump.
I find your videos the most useful. I've used a power mux before but never heard of this feature.
Glad to help!
Hi.
At 2:00 you claim that the battery will be trikcle-charged, if the load, the charger, and the battery are all in parallel. I believe you mean float-charged and not trickle-charged right? You also claim that it is bad to do so. Can you please elaborate why it is so bad to float charge a li-Ion battery? Does it pose a fire hazard, or will it just wear the battery slightly faster? How will the cell be damaged if the voltage of the celle never goes above 4.2V? Looking forward to hear your answer. And thanks for the educational content!
Thanks for your tutorial, its very helpful for me as I am currently designing a charging circuit.
However I will like to seek your opinion on this. In the case I want for example charge my batteries at 0.5C which will be about 3.45A since the battery capacity is 6,900mAH, and I am using a solar panel as input source which supplies for around 400mA. What strategy would you suggest to make this work? Are there some boost circuitry that can help amplify the input current?
Thanks.
I'm struggling to find a power path IC for a 2S battery, do you have any specific recommendations?
Thanks for the videos, this is the type of thing I hadn't thought about when I started designing my system.
What works for me is the MCP1640 which will boost the battery voltage to 5V for my load.
So when USB power is available, the MCP1640 is disabled and automatically isolates the load from the charger.
Then a diode to feed USB power to the load whilst the battery is charging. The load runs fine at 4.5V.
Admittedly I don't need more than 200 mA for charging and the load is less than that, but it works fine.
That is very interesting. I suppose you still need to monitor the voltage of the battery to cut-off its role as supply to the system if it gets below a certain voltage (say 3.3V?), would you then want to use a fuel gauge and some sort of mosfet to turn off the supply path?
Golden content, thank you.
Excellent video! Caused me to go back and reexamine a recent design that's presently having it's first-spin prototype evaluated under real-world operating conditions. Turns out I did make a mistake and my charging IC, an MCP73831, can be fooled when charging and using the device at the same time (which is an edge case; it's normally charged and then used). Since my battery charges at 200mA from a standard USB supply, the nominal load is 100mA, and the system will tolerate up to 5.5 Volts, the next spin will will incorporate your idea #2 for input bypass.
I really appreciate you taking the time to create these videos. I find many of them to be incredibly helpful.
Hah! Yeah, it always finds a way to come up and bite you. Glad you enjoyed. (Make sure to check the blog on the fixed circuit for option two, you need back to back FETs instead of one!)
@@MicroTypeEngineering Thanks! Yeah, I read the video description right after watching the video, which led me to the blog. Your content is very thorough.
regarding those power path IC s I am not sure if i understand well:
let s say my load is 1A and by battery pack charges at 2A and my external power is 2.5A
then 1A will go to the load and 1.5A to the battery? or this i think will happen
and if the load for some reason needs now 2A then the battery will then receive the remaining 0.5A right?
I had to think about in what circumstance the battery charger would be fooled into thinking the li-ion cell isn't changed due to the current draw from the device.
Lets use the example charge/draw currents.
Icharger = 400mA Idevice = 100mA
Cell is charged until V>4.2V AND I
Anyway I think this would be another solution:
Measure the current drawn by the device, and subtract that from the charger output current, to get the cell charge current.
Requires either a MCU based Li-Ion charger, or an opamp(s) to do the subtraction.
Probably not doable with a cheap ebay module, due to difficulty cutting the tracks in such a confined PCB.
So by your example is it fair to say that the method of connecting the load directly to the output of the battery could only work if the device load is less than the termination current needed by the charger? It seems like in this case the charger can not be fooled. And inversely - connecting a load directly to the battery terminal would not be safe if the current required by device is greater than the termination current the charger needs to see to terminate the charging cycle.
What I don't really understand about the powerpath ICs is the following; is the System output of these ICs a regulated output, or is it a direct throughput of the Vin or Vbat?
Cool and informative
Any suggestions for power path ICs used on 2S lipos protected by a BMS? My team is building a competition rocket and regulations encourage the use of umbilical for charging, while mandating the use of a BMS. I know usually cells in series are balance charged, but from our research it looks like, if we balance charge usually, then simply charge them in series for the one time we fly the vehicle, they shouldn't accumulate to much of a delta to cause problems. In that case we could use a standard powerpath IC made for single cells and call it a day. We just dont have much experience with this so would be good to hear suggestions from people who've worked on something similar:)
Question, does the mosfet instantly stop conducting current from the battery to the load as soon as voltage is applied to the gate
Instead of using a mosfet, would a regular switch work? It would short the load from the IC right ?
That's what I did yes, but then I needed to put a voltmeter on the battery at all times to make sure it doesn't discharge too much. I am learning.
Another issue people fail to take seriously is low battery voltage. Relying on the inbuilt protection board takes the battery voltage to a level where the capacity of the battery can be considered less than 0%, performance-wise. So when I design circuits I use the ADC of a PIC to monitor voltage and react accordingly. Anything below around 3v, the circuit is disabled and the chip shuts down. Using the battery below 3v is pointless anyway, and some chargers just won't see the battery at such a low voltage!
Nice video 👍👍
I would really Like a Video of RF Marching networks
nice sharing
Have you also tested that the battery is being charged too much?
First!
So where are the unicorns and rainbows. =D